Polymers of vinyl pyrrolidones, particularly polyvinylpyrrolidone, are useful as inert carriers or fillers for various purity sensitive active chemicals. However, such polymers in powder form experience deterioration due to oxidation when exposed to air over extended periods of time. This is a serious consideration when the polymer is employed as a carrier for certain pharmaceutically active compounds or mixtures of compounds. For example, to meet specification for drugs, the amount of oxidized impurities, such as peroxide content, in the carrier must be maintained below 400 ppm.
High molecular weight polyvinylpyrrolidone (PVP) is especially valued as a carrier or filler for active components because of its hydrophobic/hydrophilic property which provides strong bonding and dispersability of the active ingredient. Further beneficial characteristics which set apart this homopolymer include water solubility, biodegradability and film leveling properties. Accordingly, the vinylpyrrolidone polymers have a wide field of application in the agrochemical, cosmetic and pharmaceutical arts. However, a major problem encountered in the extended storage of this polymer powder manifests itself in chain length deterioration caused by relatively small amounts of oxygen entrapped with the polymer during packaging. It has been found that packaged polymer, when stored for more than 6 months often undergoes a deterioration in K value from 95 to 85 or less, which significantly affects the viscosity of subsequent polymer solutions. The molecular weights of PVP have traditionally been characterized by K-value, which is related to relative viscosity (H. Fikentcher,Cellulose-Chem., 13,58 1932).
Accordingly, it is an object of this invention to overcome the above problem by providing a storage stable vinyl lactam polymer having oxygen containing impurities less than 300 ppm while maintaining a K-value similar to the initial polymer K-value.
Another object of the invention is to additionally provide a vinyl pyrrolidone polymer which retains all of its original desirable properties after storage for extended periods of time.
These and other objects of the invention will become apparent from the following description and disclosure.
In accordance with this invention there is provided a packaging environment for delivery of a stabilized, oxygen degradable particulate polymer which comprises said polymer sealed within a receptacle the walls of which have an atmospheric oxygen permeability of less than 3.5 cc/100 sq. inch/24 hr. for a 3 mil film and a water moistened oxygen scavenging agent-enclosed in at least one separate package or packet within said receptacle which package or packet is air permeable and is exposed to the atmosphere within said sealed receptacle.
The oxygen degradable polymer of the present invention is in particulate form, eg. as a powder, granule or flake and includes any polymer which is subject to at least partial oxidation, which is undesired for its ultimate use. Such polymers include N-vinyl lactam homo- and co-polymers and particularly polyvinylpyrrolidones (PVP) of varied molecular weights having a K value of from 12 to 150. The homopolymers of vinyl pyrrolidone having a high K value are subject to chain scission when exposed to oxygen over relatively short storage periods. For example, the K value of K 90 PVP, exposed to oxygen within a sealed container for a period of 180 days, can be as low as 85 or less.
The present polymer, when prepared for shipping or storing is generally sealed in an essentially gas impervious receptacle such as a plastic bag composed of a polyamide such as Nylon, polyester or ethylene/vinyl alcohol copolymer, vinyl chloride/vinyl-idene chloride copolymer such as Saran and the like having block, alternating or random structure. Such polymer receptacles are usually in the form of bags and have a gas permeability less than 3.5 cc/100 sq. inch/24 hr. for a 3 mil film. Poly(ethylene/vinyl alcohol) and Saran bags having an atmospheric oxygen permeability less than 0.1 cc/100 sq. inch/24 hrs.for a 3 mil film are preferred. The plastic containers may also include a metal foil or film lining or laminate to additionally insure against permeability of air. Generally the polymer receptacle is loosely filled with the particulate polymer to prevent tearing or bursting during handling and-shipment. Bags, ⅔ to {fraction (9/10)} filled with polymer particles are recommended. Unavoidably, a given amount of air enters the polymer receptacle before sealing and the oxygen content entrapped therein is sufficient to cause deleterious oxidation of the polymer.
According to this invention, certain oxygen scavenging agents, containing a critical concentration of moisture are employed and are exposed to the atmosphere within the sealed receptacle but are separated from direct contact with the polymer particles. Direct contact of scavenger with the polymer is to be avoided in order to prevent polymer contamination and hence contamination of a subsequently formed polymer/active composition. This is accomplished by the use of one or more separate, air pervious packages containing the scavenging agent within the polymer receptacle The polymer containing package or packages may be integrally attached to an inner wall of the receptacle or may be freely or randomly distributed among the particles of polymer.
Suitable scavenging agents used to prevent degradation of the present polymer include ascorbic acid, iron powder, and an inorganic ferrous salt such as ferrous-halide, -nitrate or -sulfide. The scavenging agents employed herein critically contain 1 gram of water for every 1 to 100 grams of scavenger, preferably 1 gram of water/1.0 to 10 grams of scavenger and are thus employed in the form of a pliant consistency as in a paste, glue, soft wax or self-supporting cream.
Air contains about 20% oxygen by volume. The amount of scavenger employed depends on the oxygen content within the receptacle, between about 0.5 and about 1 gram of scavenger (iron powder)/liter of air is required to reduce polymer deterioration. Except for economic considerations, significantly larger amounts of scavenger, e.g. 10 grams of scavenger/liter of air can be employed, however such larger amounts of scavenger will not have any noticeable benefit in polymer stabilization.
Optionally, the scavenging agent composition used herein may additionally include a promoter to accelerate the oxygen reduction reaction. In this case, only a small amount, e.g. 1 part of promoter/200 parts of iron oxide, are employed; however, the use of up to 10 parts promotor/l part of scavenger is also within the scope of this invention. Suitable promoters include inorganic alkali and alkali earth metal salts of which the chloride, sulfide and nitrate of sodium or calcium are most desirable. Weak organic acids and bases such as acetic acid and triethanolamine promoters can also be employed as well as mixtures of the foregoing promoters if desired.
Having broadly described the present invention, reference is now made to the following examples which illustrate preferred embodiments but which are not to be construed as limiting to the scope of the invention as defined in the appended claims.